static byte[] buildDH(DHPublicKey key) {
DataByteOutputStream out = new DataByteOutputStream();
BigInteger p = key.getParams().getP();
BigInteger g = key.getParams().getG();
BigInteger y = key.getY();
int pLength, gLength, yLength;
if (g.equals(TWO) && (p.equals(DHPRIME768) || p.equals(DHPRIME1024))) {
pLength = 1;
gLength = 0;
} else {
pLength = BigIntegerLength(p);
gLength = BigIntegerLength(g);
}
yLength = BigIntegerLength(y);
out.writeShort(pLength);
if (pLength == 1) {
if (p.bitLength() == 768) out.writeByte((byte) 1);
else out.writeByte((byte) 2);
} else out.writeBigInteger(p);
out.writeShort(gLength);
if (gLength > 0) out.writeBigInteger(g);
out.writeShort(yLength);
out.writeBigInteger(y);
return out.toByteArray();
}
public static void main(String args[]) throws Exception {
Scanner cin = new Scanner(System.in);
BigInteger s, M;
int p, i;
while (cin.hasNext()) {
p = cin.nextInt();
s = BigInteger.valueOf(4);
M = BigInteger.ONE;
M = M.shiftLeft(p).subtract(BigInteger.ONE);
for (i = 0; i < p - 2; ++i) {
s = s.multiply(s).subtract(BigInteger.valueOf(2));
while (s.bitLength() > p) {
s = s.shiftRight(p).add(s.and(M));
}
}
if (s.compareTo(BigInteger.ZERO) == 0 || s.compareTo(M) == 0) {
System.out.println(0);
continue;
}
String ans = "";
while (s.compareTo(BigInteger.ZERO) > 0) {
long buf = s.mod(BigInteger.valueOf(16)).longValue();
ans += Integer.toHexString((int) buf);
s = s.divide(BigInteger.valueOf(16));
}
for (i = ans.length() - 1; i >= 0; --i) System.out.print(ans.charAt(i));
System.out.println();
}
}
private void makeKeys() {
PrimeGenerator pg = new PrimeGenerator(513, 10, sr);
do {
p = pg.getStrongPrime();
} while (p.subtract(BigIntegerMath.ONE).mod(BigIntegerMath.THREE).equals(BigIntegerMath.ZERO));
do {
q = pg.getStrongPrime();
} while (q.subtract(BigIntegerMath.ONE).mod(BigIntegerMath.THREE).equals(BigIntegerMath.ZERO));
modulus = p.multiply(q);
// Use 3 as enciphering exponent - OK since we are using salt
decipherExp =
BigIntegerMath.THREE.modInverse(
p.subtract(BigIntegerMath.ONE).multiply(q.subtract(BigIntegerMath.ONE)));
ciphertextBlockSize = (modulus.bitLength() - 1) / 8 + 1;
// Maximum size of plaintext is 6 bytes less than ciphertext
// 1 to get under modulus
// 4 for the salt
// 1 for a pad byte
plaintextBlockSize = ciphertextBlockSize - 6;
}